不同的表面处理对针织碳纤维复合材料的影响分析(英文)

纤维复合材料已经研究了数十年了。他们有着比传统材料,如钢材,优秀的多的力学性能。然而,由于相对较低的产量,梭织、编织与其3D纤维结构的复合材料被认为较难大量生产。因此,近年来,针织物在复合材料界获得了较高的关注,它的高度可塑性使针织复合材料可以直接生产制造成各种复杂形状的复合材料如管状、圆锥型等,使得材料的浪费可以降到了最低。本文使用了有表面处理和没有表面处理的纬编平针碳纤维制成复合材料。对两种复合材料的经向和纬向分别做了拉伸试验。结果显示:有表面处理的材料具有更好的拉伸性能,尤其是在wale方向上,有表面处理的复合材料比没有表面处理的复合材料的拉伸强度提高75.68%。     

Synthetic Molecular Gear Based on Double-Decker Porphyrin Complexes

New rotary molecular machines (1 and 2) were synthetically constructed from two distinct porphyrin-based rotors, a cerium(IV) bis(porphyrinate)s double-decker (CeDD) and a porphyrinatorhodium(III)-based rotor. These rotors are adjacently mounted on rotational axes aligned to near vertical as resembling the bevel-gear-shaped structure. Structural study using NMR analysis reveals that these distinct rotors are connected through a coordination bond between rhodium(III) and a pyridyl group. At temperature from 193 to 393 K, each rotor represents rotational motion driven by heat fluctuation without decomposition into the corresponding precursors in dichloromethane-d ₂ and tetrachloroethane-d ₄. Importantly, the mechanical interaction between the teeth of these rotors is strongly dependent on the central metal atom in a DD rotor and the teeth structure in a porphyrinatorhodium(III)-based rotor. Understanding such relationship between the chemical structures and mechanical interaction is of importance for generating cooperative motion in the hybrid machinery system.     

Enhanced strain hardening in elongational viscosity for HDPE/crosslinked HDPE blend. I. Characteristics of crosslinked HDPE

Blending a crosslinked high‐density polyethylene (xHDPE) enhances melt strength and strain hardening behavior in elongational viscosity of high‐density polyethylene (HDPE) to a great degree. Gel fraction of xHDPE has a stronger effect on the strain hardening than sol fraction, although sol fraction also enhances the strain hardening to some degree. Further, the xHDPE crosslinked by peroxide in a compression mold exhibits more pronounced effect than xHDPE by radiation, which is attributed to the difference in the amount of the gel fraction. The xHDPE, which enhances the strain hardening, has sparse crosslink points in the network. Moreover, it was found from linear viscoelastic measurements, such as oscillatory modulus and relaxation modulus, that the xHDPE is characterized as a critical gel, which was also supported by the result of tensile testing. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 73–78, 2002     

Synthesis and electrode performance of layered nickel dioxide containing alkaline ions

Several polymorphs of layered nickel dioxide were prepared by using the chemical insertion of alkaline ions into Li_0.10NiO₂. We used aqueous AOH (A = Li, Na, K) solutions as reducing agents. Sodium and potassium insertion resulted in hydrated layered compounds that can be classified as γ-NiOOH with high crystallinity, while lithium insertion occurred without hydration. We discuss the coordination environment around the A⁺ ions for these inserted compounds. The thermal behavior, analyzed using high temperature (HT) X-ray diffraction (XRD) and thermogravimetric (TG) measurements, indicated that heating the hydrate at 150 °C yielded its dehydrate. The electrode performance of the nickelate was studied in lithium cells. We discuss the effect of interlayer water on cell rechargeability and the similarity between these nickelate and hydrated manganese dioxide (birnessite).     

Identification and Characterization of D‐Succinylase,and a Proposed Enzymatic Method for D‐Amino Acid Synthesis

Chiral amino acids are important intermediates for the pharmaceutical industry. We have developed a novel one‐pot enzymatic method for D ‐amino acid synthesis by the dynamic kinetic resolution of N‐succinyl‐dl ‐amino acids using D ‐succinylase (DSA) and N‐succinylamino acid racemase (NSAR, EC 4.2.1.113). The DSA from Cupriavidus sp. P4‐10‐C, which hydrolyzes N‐succinyl‐D ‐amino acids enantioselectively to their corresponding D ‐amino acids, was identified for the first time by screening soil microorganisms. Subsequently, the DSA gene was cloned and overexpressed in Escherichia coli. DSA was shown to comprise two subunits with molecular masses of 26 kDa and 60 kDa. Additionally, the NSAR gene from Geobacillus stearothermphilus NCA1503, which racemizes N‐succinylamino acids, was also cloned and overexpressed in E. coli. The highly purified DSA and NSAR prepared from each recombinant E. coli were characterized and used for D ‐amino acid synthesis. A one‐pot enzymatic method converted 100 mM N‐succinyl‐dl ‐phenylalanine to D ‐phenylalanine in 91.1% conversion with 86.7% ee. This novel enzymatic method may be useful for the industrial production of many D ‐amino acids.

     

A Hexameric Ribozyme Nanostructure Formed by Double-Decker Assembly of a Pair of Triangular Ribozyme Trimers

The modular architecture of naturally occurring ribozymes makes them a promising class of structural platform for the design and assembly of three-dimensional (3D) RNA nanostructures, into which the catalytic ability of the platform ribozyme can be installed. We have constructed and analyzed RNA nanostructures with polygonal-shaped (closed) ribozyme oligomers by assembling unit RNAs derived from the Tetrahymena group I intron with a typical modular architecture. In this study, we dimerized ribozyme trimers with a triangular shape by introducing three pillar units. The resulting double-decker nanostructures containing six ribozyme units were characterized biochemically and their structures were observed by atomic force microscopy. The double-decker hexamers exhibited higher catalytic activity than the parent ribozyme trimers.     

Study of the properties of nickel oxide and nickel as precursors for the tartaric acid-NaBr-modified nickel catalyst

Nickel oxide was prepared by the decomposition of nickel hydroxide and then the nickel oxide was reduced to form the nickel catalyst. The properties of the nickel oxide and the reduced nickel were studied in relation to the enantio-differentiating ability (e.d.a.) of a tartaric acid-NaBr-modified reduced nickel catalyst. The modified nickel catalyst prepared from nickel oxide with less non-stoichiometric oxygen produced a high e.d.a. for the hydrogenation of methyl acetoacetate. The high crystallinity of the nickel oxide and the resultant nickel would be required to attain a high e.d.a.     

The effect of thickness on the steady-state creep properties of freestanding aluminum nano-films

To clarify the effects of film thickness on the creep properties of nano-films we conducted tensile creep experiments on freestanding aluminum films with thickness values in the range ～100–800 nm at room temperature. The nano-films showed typical creep behavior comprising transient, steady-state, and accelerated creep stages. The steady-state creep exponents of the 100–800 nm thick specimens were 0.84–2.7 in the stress range 30–120 MPa, which are close to the value for diffusion creep (1). Creep deformation clearly shows a thickness effect: the steady-state creep rate increases as the thickness decreases from 800 to 400 nm, shows a peak in the range 400–200 nm, and then decreases in the 200–100 nm thickness range. The creep experiments under a small stress of 1 MPa show a negative strain rate, indicating the presence of a driving force to reduce the surface area due to surface tension. The explanation for the thickness effect is as follows. Since the ratio of surface and grain boundary area to volume increases with decreasing thickness, diffusion creep along these paths is enhanced, resulting in an increase in the creep rate. As the thickness decreases to 200–100 nm, however, the surface tension effect to reduce the surface area becomes dominant, decreasing the creep rate. In addition, the creep rate of the nano-films is about two or three orders of magnitude smaller than that of the bulk material dominated by the dislocation creep mechanism.     

Processability and mechanical properties for binary blends of PP and LLDPE produced by metallocene catalyst

Processability at extrusion coating and mechanical properties of the films obtained are investigated by means of linear and nonlinear rheological measurements and tensile tests for blends of polypropylene (PP) and linear low‐density polyethylene (LLDPE). Both materials are produced by metallocene catalyst. The processability of PP is found to be improved by the addition of LLDPE; the blend shows low level of motor torque and head pressure in an extruder and small level of neck‐in as compared with pure PP. Further, the anisotropy of ultimate tensile strength, which is prominent for PP, is reduced by blending with LLDPE. As a result, the blend having 20 wt % of LLDPE shows appropriate properties in the molten state for extrusion coating and in the solid state as a film. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009